Senate Republican leaders have more work to do to sell their members on a two-year budget deal unveiled late Monday night.

GOP senators highlighted parts of the package meant to offset increased defense and domestic spending as their chief concerns. Their comments were followed by a blistering critique of the deal from the conservative groups Heritage Action for America and the Club for Growth. Sen. Jeff Flake, R-Ariz., told CQ Roll Call following a Monday evening caucus meeting he has some “concerns” about the deal explained to GOP senators.

“The mandatory offsets aren’t mandatory or big enough,” Flake said after leaving the meeting. "There are some to Social Security disability — some reforms — that are desperately needed. We’ll have to see if those are actually real.

“And we’ll have to see if the health care offsets are real or if they’re just gimmicks — you know, squeezing docs, squeezing providers — that we end up backfilling later,” he said. “That does us no good.”

“If you look at it in a debt limit context, you actually [should] reduce spending,” Portman told reporters when asked about his concerns. “That’s the idea, to as you raise the debt limit, address the underlying debt problem that we have.”

And one of the chamber's most conservative members, GOP Sen. Tim Scott of South Carolina signaled he is opposed to the plan, saying parts of it appear “salacious” to him.

One major flaw, he said, “is that we trim around Social Security and disability.”

Asked if anything described in the meeting would significantly slash entitlement program spending, Scott replied: “Not at all.”

Scott said he does see some “things that are positive” in the deal. “Overall, I think some of us see some real progress being made on issues we’ve been fighting for for some time,” he said.

But Heritage Action and the Club for Growth see few reasons to be upbeat about the overall measure.

“This budget and debt deal is being brokered by a lame duck speaker and a lame duck president," Heritage Action CEO Michael A. Needham and Club for Growth President David McIntosh said in a joint statement. "It represents the very worst of Washington — a last minute deal that increases spending and debt under the auspices of fiscal responsibility. If this deal moves forward, it will undermine efforts to unite the party by those promising to advance serious policy reforms.

Needham and McIntosh want House GOP leaders to wait until Rep. Paul D. Ryan, R-Wis., officially has the gavel to move any spending package. They dubbed this measure a "zombie budget deal.”